1. Programming commands in their raw state as input by a programmer. Some programming languages allow the commands to be executed on the fly by a program interpreter. Other languages require the commands to be compiled into executable programs (binaries) before they can be used. In the UNIX/Linux world, some software is distributed as source code only; other packages include both source and binaries; still others are distributed in binary format only. From I-gloss

2. In a high-level programming language, the typed program instructions that progammers write before the program is compiled or interpreted into machine language instructions the computer can execute. From QUECID

3. The form in which a computer program is written by the programmer. Source code is written in some formal programming language which can be compiled automatically into object code or machine code or executed by an interpreter. From Linux Guide @FirstLinux